Ink jet printers are well known in the art. Generally, an ink jet printer includes an array of nozzles or orifices, a supply of ink, a plurality of thin channels connecting the array of nozzles with the ink supply, respectively, a plurality of ejection elements (typically either expanding vapor bubble elements or piezoelectric transducer elements) corresponding to the array of nozzles and suitable driver electronics for controlling the ejection elements. Typically, the array of nozzles and the ejection elements along with their associated components are referred to as a print head. It is the activation of the ejection elements that causes drops of ink to be expelled from the nozzles. The ink ejected in this manner forms drops which travel along a flight path until they reach a print medium such as a sheet of paper, overhead transparency, envelope or the like. Once they reach the print medium, the drops dry and collectively form a print image. Typically, the ejection elements are selectively activated or energized as relative movement is provided between the print head and the print medium so that a predetermined or desired print image is achieved.
Generally, there are two methods available for integrating the print head and the ink supply. A widely adopted method combines the following into a disposable cartridge: the print head, ink supply, ink delivery system and a contact pad for receiving control signals from the ink jet printer. In this manner, a fresh cartridge may be installed when the ink supply of the current cartridge has been consumed. On the other hand, the print head and the ink supply may be located remotely from each other.
To keep an ink jet printer in proper working order, it is necessary to control the pressure at which ink is delivered from the supply to the print head. If the pressure is too high, then there is a risk that ink will leak out of the print head. On the other hand, if the pressure is too low, then there is a risk that the capillary forces on the ink in the ink channels may not be sufficient to draw ink down from the supply. Therefore, it is desirable to maintain the pressure at the print head (commonly referred to as back pressure) within a predetermined range. In most ink jet printers the back pressure is set just below atmospheric pressure. Since back pressure also influences ink drop size, maintaining the back pressure within a narrow predetermined range has the added benefit of producing individual ink drops of uniform size. This also directly contributes to increased print quality.
Recently, the postage meter industry and other envelope printing industries have begun to incorporate ink jet printers. A typical postage meter (one example of a postage printing apparatus) applies evidence of postage, commonly referred to as a postal indicia, to an envelope or other mailpiece and accounts for the value of the postage dispensed. As is well known, postage meters include an ascending register, that stores a running total of all postage dispensed by the meter, and a descending register, that holds the remaining amount of postage credited to the meter and that is reduced by the amount of postage dispensed during a transaction.
Generally, the postage meter may be incorporated into a mailing machine, which is also well known in the art, for automated handling of the mailpieces. Mailing machines are readily available from manufacturers such as Pitney Bowes Inc. of Stamford, Conn. USA and often include a variety of different modules, which automate the processes of producing mailpieces. The typical mailing machine includes a variety of different modules or sub-systems where each module performs a different task on a mailpiece, such as: singulating (separating the mailpieces one at a time from a stack of mailpieces), weighing, sealing (wetting and closing the glued flap of an envelope), applying evidence of postage, accounting for postage used performed by the postage meter), feeding roll tape or cut tape strips for printing and stacking finished mailpieces. However, the exact configuration of each mailing machine is particular to the needs of the user. Customarily, the mailing machine also includes a transport apparatus, which feeds the mailpieces in a path of travel through the successive modules of the mailing machine.
In high volume mailing machines it is desirable to have separate mailpiece and tape feed paths. In this manner, the structure of the mailing machine may be optimized for the diverse requirements of feeding mailpieces and tape. That is, the transport apparatus includes an assembly best suited for feeding mailpieces and another assembly best suited for feeding tape. Examples of such mailing machines are described in U.S. Pat. Nos. 5,467,709 and 5,696,829. Also, to assist in registering the top edge of the mailpiece, the mailing machine often includes a feed deck that is inclined slightly from horizontal. In this manner, gravity assists by inducing the mailpieces to slide down the inclined feed deck until the top edge of the mailpiece abuts a substantially vertical registration wall.
Although such mailing machines work generally well, some drawbacks have been identified. In such high volume mailing machines it is possible to print large numbers of envelopes (180 to 240) per minute which leads to a very large number of envelopes printed on a daily basis. Thus, the rate of ink consumption is high. As a result, the ink cartridges do not provide an economical method of supplying ink and need to be replaced frequently by the operators. Furthermore, the disposable nature of the cartridges does not lend itself to cost effective operation because of the amount of material (print head, contact pad, ink delivery system, etc.) that is thrown away.
Therefore, there is a need for a postage printing apparatus, such as a mailing machine, that incorporates a large capacity ink supply, controls back pressure and is capable of printing in two positions, one for mailpieces and the other for tape.